Heat-resistant resins such as polyimide and polybenzoxazole have a high level of heat resistance and electrical insulating properties and therefore are used for surface protective films for semiconductor devices such as LSI (Large Scale Integration) and interlayer dielectric films. In recent years, as semiconductor devices become finer, surface protective films, interlayer dielectric films and so on, have been required to be formed at a resolution of few μm. In such applications, therefore, positive-type photosensitive polyimide or polybenzoxazole which can be subjected to fine processes is used.
On the other hand, there is proposed a positive-type photosensitive resin composition comprising novolac resin, which is widely used for photoresists, and a polyimide precursor or a polybenzoxazole precursor, and a quinone diazide compound (see for example Patent Document 1). However, thermally cured films produced with such a resin composition are very brittle and insufficient in mechanical properties, particularly in elongation or strength, as compared with those of conventional polyimide or polybenzoxazole. There are also proposed positive-type photosensitive resin compositions comprising a novolac resin, and a polyamide precursor or a polybenzoxazole precursor, and a quinone diazide compound, and a polyfunctional methylol compound (see for example Patent Documents 2 to 4). However, such resin compositions have poor mechanical properties or storage stability and the problem of significant changes in sensitivity. For these reasons, it has been difficult to use these resin compositions in place of photosensitive polyimide or polybenzoxazole in such applications as surface protective films for semiconductor devices and interlayer dielectric films.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2005-352004 (claim 1)    Patent Document 2: JP-A No. 2005-062764 (claim 1)    Patent Document 3: JP-A No. 2005-250160 (claim 1)    Patent Document 4: JP-A No. 2006-285037 (claim 1)